1. Field of the Invention
The present invention relates to electrical isolation of an endoscope video camera, and more particularly relates to a isolation circuit for electronic endoscopic camera apparatus which is uniquely simple and low in cost.
2. Background Information
Endoscopic video systems are now used with endoscopes in general surgery. The endoscope may be a passive optical device which is attached to an external image sensor or may contain electronic circuitry including a charge coupled device (CCD) image sensor mounted at the distal end or elsewhere. An umbilical connects the sensor-endoscope assembly, (hereinafter referred to as the camera head) to a video processing support unit that obtains operating power from the commercial power mains, and provides a ground-reference video output. New and more demanding safety regulations require that electrical isolation be provided between the camera heads which makes physical contact with the patient and the processing electronics.
One method of providing such isolation is through the use of a transformer isolation circuit applied in the electrical path between the camera head and processing electronics. In this method, the camera head assembly is connected by an umbilical support unit with a ground reference video output that is connected to commercial powers A transformer isolation circuit is provided by a plurality of separate circuits, each dedicated to a particular signal required by the video system.
The CCD image sensor requires a large number of drive signals, some of which are high frequency, over 10 MHz. Furthermore, the CCD output signal also has a high frequency pixel rate. This complicates the design of previous isolation circuits and methods have been devised to find ways to reduce the required number, and bandwidth, of such circuits as shown in the U.S. Pat. No. 4,931,867 of Kikuchi issued Jun. 5, 1990. This method requires additional, redundant circuitry to be added to the isolation part of the endoscopic video system.
Another attempt to reduce noise in video signal transformer isolation circuits is by driving the transformer differentially and providing DC restoration with a so called "one pixel clamp" as disclosed in U.S. Pat. No. 4,868,647 of Uehara et al issued Sep. 19, 1989. This patent also shows the method of driving a transformer with a carrier wave modulated by the CCD output after it has been converted to the base-band by double correlated sampling. Uehara et al also disclose using a delay line and differential drive technique to suppress noise from the CCD reset pulse. These techniques add complexity and cost to the overall isolation circuitry. It would be more desirable to develop an isolation system that requires a minimum overall number and variety of components without unreasonable compromise to performance.
It is one object of the present invention to provide a medical electronic endoscope system which can sufficiently guarantee the safety of the patient by means of an electrical isolation of the endoscope.
Another object of the present invention is to provide a medical electronic endoscope system, having isolation circuitry that is low in cost and uses a minimum variety of components.
Still another object of the present invention is to provide electrical isolation of a medical electronic endoscope system that uses low-cost pulse transformer circuitry.
Yet another object of the present invention is to provide electrical isolation of medical endoscopic camera electronics using technology that maintains strict leakage and insulating isolating requirements with simple electronic circuitry.
Still another object of the present invention is to provide a medical endoscopic camera system electronics with electrical isolation that suppresses noise in CCD output signal from the CCD reset pulse.
Yet another object of the present invention is to provide electrical isolation of medical endoscopic camera electronics that can process and isolate bi-directional data signals.
Still another object of the present invention is to provide isolation of medical endoscopic camera electronics by isolating open collector bi-directional data signal lines using electronic shunts on the primary and secondary side of a pulse transformer.
Still another object of the present invention is to provide electrical isolation of medical endoscopic camera electronics that isolate timing signals by converting the timing signals to leading and lagging spikes which are reconstructed on the secondary side of a pulse transformer.